1. Field of the Invention
The present invention relates generally to water heaters and boilers, and more particularly, but not by way of limitation, to such a water heater or boiler which is constructed to provide a variable heat energy output which is continuously variable over a wide range.
2. Description of the Prior Art
Conventional water heater technology utilizes a burner designed to operate at a fixed flow rate of combustion air and fuel gas to the burner. Such a water heater cycles on and off in response to a control system which monitors the temperature of water in a storage tank or elsewhere in various conduits of the water supply system. One example of such a typical prior art system which is presently being marketed by the assignee of the present invention is that shown in U.S. Pat. Nos. 4,723,513 and 4,793,800 to Vallett et al., the details of which are incorporated herein by reference.
It has been recognized that, in circumstances where there is a substantially varying demand for heat input to the water supply system, greater energy efficiencies can be achieved through the use of a water heater which is capable of operating at different energy inputs. One example of such a system is that sold by Lochinvar Corporation, the assignee of the present invention, under the trademark COPPER-FIN II(copyright). The Lochinvar COPPER-FIN II(copyright) system utilizes a plurality of staged burners which can be brought on-line or taken off-line as the demand for heat energy changes. The Copper-Fin II(copyright) unit includes multiple banks, for example, first, second, third and fourth stages. It initially turns on all four stages of burners, and as it approaches the desired temperature, it sequentially shuts off units to decrease the input energy. This type of system provides variable input, but it is not continuously variable. Instead the input can be changed only in substantial increments corresponding to the heat output of one burner stage.
The prior art has also included proposals for water heaters having continuously variable output over a range of outputs. Two such systems are shown in U.S. Pat. No. 4,852,524 to Cohen and U.S. Pat. No. 5,881,681 to Stuart. These systems, which have been marketed by Aerco International, Inc. under the Benchmark name, utilize a nozzle mix burner which receives independent streams of combustion air and fuel gas. A fuel/air valve is utilized to simultaneously control the flow of air through the air line and fuel through the fuel line so as to provide a varying input of fuel and air while maintaining a constant fuel to air ratio. The blower speed remains constant on these systems.
There is a continuing need in the art for improved energy efficiency in water heaters and boilers. The present invention is directed to improvements which provide a continuously variable heat output from a pre-mix burner, as contrasted to systems like that of Stuart, which utilize a nozzle mix burner.
A water heater apparatus includes a water conduit having an inlet and an outlet. A primary heat exchanger has a water side which defines a portion of the water conduit. A burner is operatively associated with the primary heat exchanger for heating water in the water side of the primary heat exchanger. A variable flow blower provides pre-mixed combustion air and fuel gas to the burner at a controlled blower flow rate within a blower flow rate range.
The blower speed is controlled in response to water temperature which may be sensed at any one of several locations within the water supply system.
The variable flow blower preferably includes an electric motor and a variable frequency drive which varies the speed of the electric motor and thus the flow rate of the blower by varying a frequency of an electrical power signal provided to the electric motor.
The system may also include a recirculation conduit connected to the water conduit downstream and upstream of the primary heat exchanger. A recirculation valve is disposed in the water conduit. A water temperature sensor is provided for sensing water temperature along the water conduit. A controller is operatively associated with the water temperature sensor and the recirculation valve for varying a position of the recirculation valve in response to the temperature sensor to maintain the temperature of water entering the primary heat exchanger above a pre-determined value to prevent condensation of combustion products in the primary heat exchanger.
In another embodiment of the invention, a water heater apparatus is provided which includes a burner and a primary heat exchanger having an exterior surface exposed to the burner for receiving heat from the burner. The primary heat exchanger has an inner flow path for flowing water through the heat exchanger. A recirculation conduit communicates a water outlet with a water inlet and bypasses the heat exchanger. A recirculation valve is disposed in the recirculation conduit. A temperature sensor is disposed in one of the inner flow path and the recirculation conduit. A controller is operably associated with the temperature sensor and the recirculation valve for varying a position of the recirculation valve in response to the water temperature sensor.
Various methods of heating water utilizing the systems just described are also disclosed.
Accordingly, it is an object of the present invention to provide improved water heaters and boilers capable of operation at a heat energy output which varies over a relatively wide range.
Another object of the present invention is the provision of water heaters and boilers having improved energy efficiency.
And another object of the present invention is the provision of a water heater or boiler including a recirculation system for preventing condensation of combustion products on the exterior of a primary heat exchanger of the system.
Other and further objects, features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the following disclosure when taken in conjunction with the accompanying drawings.